Archives

The atomic radii of first group elements are given below : [Group-I element – Atomic Radii (pm)] Na – 86, K – 231, Rb – 244, Cs – 282 State the reason behind the observed trend in the above elements.

I) Group 1 elements Li Na K Rb Cs Atomic radius (pm) 152, 186, 231, 244, 262 ii) The elements Li has the smallest atom (atomic radius 152 Pm)... View Article

Define electropositivity

Electro positivity can be defined as the tendency of an atom to donate electrons and form positively charged cations. Electropositivity is... View Article

How are covalent bonds formed?

Covalent bonds are formed by the sharing of electrons between two atoms so that both can achieve a completely filled outermost shell. The pair of... View Article

List two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed.

Two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed are as follows: Number of turns in the... View Article

State the purpose of soft iron core used in making an electromagnet.

The purpose of soft iron core used in making an electromagnet is its property of losing all its magnetism when the current in the coil is... View Article

Draw a labelled diagram to show how an electromagnet is made.

It works on the magnetic effect of current. It consists of a long coil of insulated copper wire wrapped around a soft iron core that gets... View Article

What is an electromagnet? List any two uses.

Electromagnets are made out of a coil of wire (wire curled in series). This is more effective in producing a magnetic field than just a wire... View Article

An object 4.0 cm in size, is placed 25.0 cm in front of a concave mirror of focal length 15.0 cm. (i) At what distance from the mirror should a screen be placed in order to obtain a sharp image? (ii) Find the size of the image. (iii) Draw a ray diagram to show the formation of image in this case.

Height of the object, h1 = 4 cm Distance of the object from the mirror u = −25 cm Focal length of the mirror, f = −15 cm To find: (i) Distance... View Article

Draw a ray diagram in each of the following cases to show the formation of image, when the object is placed: (i) between optical centre and principal focus of a convex lens. (ii) anywhere in front of a concave lens. (iii) at 2F of a convex lens. State the signs and values of magnifications in the above mentioned cases (i) and (ii).

Ray diagrams to show the formation of image, when the object is placed: (i) Between optical centre and principal focus of a convex lens.... View Article

Why are the traits acquired during the lifetime of an individual not inherited? Explain.

Acquired characters are the traits acquired by an organism during his lifetime, based on lifestyle. These traits are not passed from one... View Article

What is the law of dominance of traits? Explain with an example.

In heterozygotes, one trait will suppress the expression of another trait for the same characteristics. An allele that expresses its... View Article

Describe in brief how urine is produced in human body.

The mechanism of urine formation involves the following steps: Glomerular filtration occurs in the glomerulus where blood is filtered. This... View Article

Name the organs that form the excretory system in human beings

The organs that form the excretory system in human beings are kidney, renal arteries, renal veins, ureter, urinary bladder, and urethra.The most... View Article

Draw a diagram of human respiratory system and label – pharynx, trachea, lungs, diaphragm and alveolar sac on it.

The human respiratory system is a system of organs responsible for inhaling oxygen and exhaling carbon dioxide in humans. The important... View Article

Why is there a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain.

The rate of breathing in aquatic organisms is much faster than in terrestrial organisms because aquatic animals breathe from the oxygen dissolved... View Article

Define atomic size. Give its unit of measurement. In the modem periodic table what trend is observed in the atomic radius in a group and a period and why is it so?

Atomic Size is the distance between the centre of an atom i.e from the nucleus to the outermost (valence) shell of that atom. Atomic size is... View Article

The position of certain elements in the Modem Periodic Table are shown below. Using the above table answer the following questions giving reasons in each case: (i) Which element will form only covalent compounds? (ii) Which element is a non-metal with valency 2? (iii) Which element is a metal with valency 2? (iv) Out of H, C and F which has largest atomic size? (v) To which family does H, C and F belong?

(i) Element E is Silicon. It will form only covalent bonds only. The outermost orbit of silicon has 4 electrons and needs 4 more electrons to... View Article

Carbon cannot reduce the oxides of sodium, magnesium and aluminium to their respective metals. Why? Where are these metals placed in the reactivity series? How are these metals obtained from their ores? Take an example to explain the process of extraction along with chemical equations.

According to the reactivity series, both sodium and magnesium as well as aluminium are more reactive than carbon as these elements are placed... View Article

A V-I graph for a nichrome wire is given below. What do you infer from this graph Draw a labeled circuit diagram to obtain such a graph.

The V−I graph for a nichrome wire shows a straight line, which means the resistance of the wire remains constant when the current supply is... View Article

Draw a labelled diagram to show (i) reddish appearance of the sun at the sunrise or the sunset and (ii) white appearance of the sun at noon when it is overhead.

(i) During sunrise, the light rays coming from the Sun have to travel a greater distance in the earth’s atmosphere before reaching our eyes. In... View Article

M	T	W	T	F	S	S
		1	2	3	4	5
6	7	8	9	10	11	12
13	14	15	16	17	18	19
20	21	22	23	24	25	26
27	28	29	30